Black Corals in Peril

Written by Sam Kahng, University of Hawaii

Figure 1. Snowflake coral saturating the roof of a ledge with millions of polyps extended while feeding at 40 feet off Pupukea. Photo courtesy of Sam Kahng.

Formally known as Carijoa riisei, this alien species is already sweeping through the Au’au Channel between the islands of Maui and Lanai like a silent blizzard. In 2001-2004, deepwater surveys in the Au’au Channel using the Pisces V submersible supported by the Hawaii Undersea Research Laboratory (HURL) determined that >50% of all black coral colonies below 230 feet had snowflake coral overgrowth with most being completely smothered and dead (Figure 2). Less than 15% of the sunlight penetrates these depths so the deep reef is permanently shaded. Scientists worry that black coral, Hawaii ‘s state gemstone which accounts for several million dollars worth of jewelry sales statewide each year, could suffer large scale mortality throughout the Hawaiian Archipelago.

The problem with snowflake coral is that it can grow very quickly (up to an inch every two weeks) and smothers other slower growing organisms. Black corals grow to over 10 feet tall, however, they grow much slower